Protection of electrical components against overcurrent conditions is well known. Typical traditional approaches include the use of fuses or circuit breakers that detect an excessive flow of electrical current and either self destruct or mechanically open to disconnect the source of electrical current from consuming or conducting devices potentially detrimentally affectable by the overcurrent.
Such traditional fuses and breakers are typically insufficiently rapid in reaction and often times are possessed of an excessively large "blow" or "tripping" current capacity to provide protection from potentially damaging current flows lower than can be protected against, when considered as candidates for providing protection to sophisticated electronic circuits having overcurrent susceptible solid state components. More recently, response times in the microseconds, and preferably in less than a microsecond, are desirable in protecting particularly sensitive solid state circuitry devices. Traditional mechanical or quasi mechanical systems simply cannot respond with the desired rapidity.
Additionally, modern solid state circuits often require relatively low electrical currents for operation and in any event do not tolerate significant current excesses even briefly without damage. Traditional mechanical circuit breakers and fuses frequently are possessed of a value for the current required to trip such traditional devices substantially in excess of the current that can be tolerated reasonably by the solid state circuitry being protected. Accordingly, an overcurrent protection means and method for triggering overprotection in an electronic solid state circuit within a time desirably short and/or at a desirably low trip current could find substantial commercial application.
Many present day electrical current configurations can be susceptible to electrical noise and particularly to so-called common mode noise, that is, electrical noise generally equally present throughout a circuit. It is desirable that overcurrent protection be substantially tolerant of common mode noise to forestall spurious circuit shutdowns due to misdetection of common mode noise as an overcurrent situation. A current interrupter substantially tolerant of common mode noise could find substantial utility in the design of electrical circuitry.
Particularly, a common mode noise tolerant current overprotection system useful for examining electrical current flowing through a circuit at a point before the current encounters the current sensitive electronic components being protected, that is a sourcing system for control, and also for a sinking system for control wherein the examination of current occurs after the current flows through the load or on the ground side of load, could find substantial utility.
Various other sourcing system means have been suggested in the art for detecting and responding to an overcurrent or overvoltage in solid state circuitry. Examples of such proposals appear to be found in U.S. Pat. Nos. 3,303,388; 3,603,843; 4,336,563; 4,204,148; 4,135,223; and 3,924,159. But these proposals appear to be susceptible to variations in control or system overcurrent protection as a result of drift associated with the operating components as a function of temperature, total current and the like. None appear to show or suggest an optical, current flow protector inherently uniform irrespective of temperature or current flow through the solid state circuitry.